Various oil and gas well drilling and servicing operations benefit from inducing vibrations in the drillstring and/or workstring used to conduct the operation, referred to herein as the “drillstring.” Examples include horizontal well drilling, in which the vibration induced in the drillstring greatly reduces downhole friction, and permit transfer of drillstring weight to the bit or other downhole device in order to effectively carry out downhole operations.
Various tools currently exist to induce downhole drillstring vibrations. Examples include tools which fundamentally operate by inducing pulses in the drilling fluid stream, by momentarily reducing flow area, then increasing it again. Such “hydraulic” tools generally do not permit passage of any downhole tools through the vibratory tool, because as a function of their mode of operation the bore is partially obstructed; as a result, downhole logging tools, fishing tools or any other type of tool cannot be used below the drillstring depth of the vibratory tool. This and other limitations exist in connection with currently known tool designs.